A virtual image display device (an image display device) for presenting a two-dimensional image formed by an image forming device as an enlarged virtual image to a viewer through a virtual image optical system is known from JP 2006-162767 A, for example. As shown in the conceptual diagram in FIG. 24, this image display device 100′ includes: an image forming device 111 having pixels arranged in a two-dimensional matrix; and an optical device (a light guiding unit) 120 that receives light emitted from the pixels of the image forming device 111, and guides and emits the light. The optical device 120 includes: a light guide panel 121 that causes incident light to propagate therein by total reflection, and then emits the light; a first deflecting unit 130 (formed with a single light reflecting film, for example) that reflects the light that has entered the light guide panel 121 so that the light that has entered the light guide panel 121 is totally reflected inside the light guide panel 121; and a second deflecting unit 140 (formed with a multi-layer light reflecting film having a multi-layer stack structure, for example) that causes the light having propagated inside the light guide panel 121 by total reflection to exit from the light guide panel 121. If an HMD is formed with such an image display device 100′, the weight and the size of the apparatus can be reduced.
Also, a virtual image display device (an image display device) that uses hologram diffraction gratings to present a two-dimensional image formed by an image forming device as an enlarged virtual image to a viewer through a virtual image optical system is known from JP 2007-094175 A, for example. As shown in the conceptual diagram in FIG. 25, this image display device 200′ basically includes an image forming device 111 that displays an image, and an optical device (a light guiding unit) 220 that receives light displayed on the image forming device 111 and guides the light to an eye 21 of a viewer. Here, the optical device 220 includes a light guide panel 221, and a first diffraction grating member 230 and a second diffraction grating member 240 that are formed with reflective volume hologram diffraction gratings provided on the light guide panel 221.
As an image is displayed on the image display device 100′ or 200′, a viewer can see the displayed image superimposed on an external image.